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pp-web / pp / examples / auto_diff.py

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#!/usr/bin/env python
# File: auto_diff.py
# Author: Vitalii Vanovschi
# Desc: This program demonstrates parallel computations with pp module
# using class methods as parallel functions (available since pp 1.4).
# Program calculates the partial sums of f(x) = x-x**2/2+x**3/3-x**4/4+...
# and first derivatives f'(x) using automatic differentiation technique.
# In the limit f(x) = ln(x+1) and f'(x) = 1/(x+1).
# Parallel Python Software: http://www.parallelpython.com

import math
import sys
import pp


# Partial implemenmtation of automatic differentiation class


class AD(object):

    def __init__(self, x, dx=0.0):
        self.x = float(x)
        self.dx = float(dx)

    def __pow__(self, val):
        if isinstance(val, int):
            p = self.x**val
            return AD(self.x**val, val*self.x**(val-1)*self.dx)
        else:
            raise TypeError("Second argumnet must be an integer")

    def __add__(self, val):
        if isinstance(val, AD):
            return AD(self.x+val.x, self.dx+val.dx)
        else:
            return AD(self.x+val, self.dx)

    def __radd__(self, val):
        return self+val

    def __mul__(self, val):
        if isinstance(val, AD):
            return AD(self.x*val.x, self.x*val.dx+val.x*self.dx)
        else:
            return AD(self.x*val, val*self.dx)

    def __rmul__(self, val):
        return self*val

    def __div__(self, val):
        if isinstance(val, AD):
            return self*AD(1/val.x, -val.dx/val.x**2)
        else:
            return self*(1/float(val))

    def __rdiv__(self, val):
        return AD(val)/self

    def __sub__(self, val):
        if isinstance(val, AD):
            return AD(self.x-val.x, self.dx-val.dx)
        else:
            return AD(self.x-val, self.dx)

    def __repr__(self):
        return str((self.x, self.dx))


class PartialSum(object):

    def __init__(self, n):
        """
        This class contains methods which will be executed in parallel
        """

        self.n = n

    def t_log(self, x):
        """
        truncated natural logarithm
        """
        return self.partial_sum(x-1)

    def partial_sum(self, x):
        """
        partial sum for truncated natural logarithm
        """
        return sum([float(i%2 and 1 or -1)*x**i/i for i in xrange(1, self.n)])


print """Usage: python auto_diff.py [ncpus]
    [ncpus] - the number of workers to run in parallel,
    if omitted it will be set to the number of processors in the system
"""

# tuple of all parallel python servers to connect with
#ppservers = ("*",) # auto-discover
#ppservers = ("10.0.0.1","10.0.0.2") # list of static IPs
ppservers = ()

if len(sys.argv) > 1:
    ncpus = int(sys.argv[1])
    # Creates jobserver with ncpus workers
    job_server = pp.Server(ncpus, ppservers=ppservers)
else:
    # Creates jobserver with automatically detected number of workers
    job_server = pp.Server(ppservers=ppservers)

print "Starting pp with", job_server.get_ncpus(), "workers"

proc = PartialSum(20000)

results = []
for i in range(32):
    # Creates an object with x = float(i)/32+1 and dx = 1.0
    ad_x = AD(float(i)/32+1, 1.0)
    # Submits a job of calulating proc.t_log(x).
    f = job_server.submit(proc.t_log, (ad_x, ))
    results.append((ad_x.x, f))

for x, f in results:
    # Retrieves the result of the calculation
    val = f()
    print "t_log(%lf) = %lf, t_log'(%lf) = %lf" % (x, val.x, x, val.dx)

# Print execution statistics
job_server.print_stats()

# Parallel Python Software: http://www.parallelpython.com